Ignition systems



Oct. 15, 1968 N. A. PARISH IGNITION SYSTEMS Filed May 2, 1966,

HIGH

vomes GENERATOR United States Patent 3,406,314 IGNITION SYSTEMS Norman Arthur Parish, Hemel Hempstead, England, as-

signor to Rotax Limited, London, England, a British company Filed May 2, 1966, Ser. No. 546,809 3 Claims. (Cl. 315-209) ABSTRACT OF THE DISCLOSURE In a spark ignition system, a capacitor is charged so that the voltage across it increases, and a voltage sensitive device is connected in the circuit across the capacitor so as to conduct when the voltage across the capacitor reaches a predetermined value. A transformer is provided for turning on a trigger device as soon as the capacitor starts to discharge through the voltage sensitive device, the trigger device then permitting the capacitor to discharge through a spark plug. A second transformer has its primary winding in series with the voltage sensitive device, and its secondary winding connected to another trigger device controlling another spark plug, and switch means is provided for determining which trigger device is switched to conduction when the capacitor starts to discharge through the voltage sensitive device.

This invention relates to ignition systems.

In the accompanying drawings, FIGURE 1 is a circuit diagram illustrating one example of the invention, and FIGURE 2 illustrates a modification of FIGURE 1.

Referring to FIGURE 1, there are provided terminals 11, 12 which in use are connected to a D.C. source so as to be negative and positive respectively. The terminal 11 provides one input to a high voltage generator whilst the terminal 12 is connectible alternatively to terminals 13, 14. The terminals 13, 11 are interconnected through parallel circuits one of which contains a diode and a relay coil 16, and the other of which contains a capacitor 17. Moreover, the terminal 14 is connected to a point intermediate the diode 15 and relay 16, and the terminal 13 is connected through an indicator 18 to the other input terminal of the generator 10.

One output terminal of the generator 10' is connected to an earthed line 21, and the other of which is connected to an output terminal 22 through a diode 23 in series with a breakdown device 24 of the kind surrounded by a band 25, the arrangement being such that the device 24 can be triggered by a voltage applied to the band 25. The circuit includes a further output terminal 26 which is connected to the cathode of the diode 23 through a breakdown device 27 having a band 28.

Points intermediate the diode 23 and the devices 24, 27 are connected to the earth line 21 through three parallel paths, the first of which contains a capacitor 29, the second of which contains a resistor 31, and the third of which contains in series a control gap 32, a resistor 33, a primary winding 34 of a first transformer, and a primary winding 35 of a second transformer. The first and second transformers having secondary windings 36, 37, one end of each of the windings 36, 37 being connected to the line 21, and the other ends of the windings 36, 37 being connected respectively to the bands 25, 28. Moreover, the transformers are provided with tertiary windings 40, 38 which have one end connected to a relay contact 39 operable by the relay 16, the arrangement being such that when the relay 16 is not energised the contact 39 bridges the winding 38, but when the relay 16 is energised the contact 39 bridges the winding 40.

A point intermediate the terminals 22, 26 is earthed, and the nature of the terminals is such that they can be ice connected to spark plugs respectively so that when they are connected the spark plugs will have one side connected to the device 24 or the device 27, and their other side earthed. Resistors 41, 42 are provided between the terminals 22, 26 and earth, so that in use these resistors are connected across the spark plugs to protect the discharge circuit.

In use, assume for the moment that the terminal 12 is connected to the terminal 13, so that the relay 16 is not energised. The terminals 13, 11 provide an input to the generator 10, the components 17, 18 being provided to minimise radio interference. The generator 10' may be of any convenient known form, and may for example comprise a transformer wherein current flow to the primary winding is interrupted by an interrupter, or by a circuit employing transistors. Thus, the generator produces a series of high voltage pulses which flow through the diode 23 to charge the capacitor 29. When the charge on the capacitor 29 reaches a predetermined value, the gap 32 will break down, and the capacitor 29 will start to discharge through the gap 32, resistor 33 and windings 34, 35. Because the winding 38 is short-circuited, the second transformer will not have an output pulse produced in its secondary winding 37, but a pulse will be produced in the secondary winding 36, which will cause the device 24 to become conductive. The capacitor discharge current is now diverted through the device 24 and the plug connected to the terminal 22 to provide the required spark.

If a spark is required at the plug connected to terminal 26, then the terminal 12 is connected to the terminal 14. The circuit to the generator 10 is unaltered, but the relay 16 is now energised, so that when the gap 32 breaks down, the winding 40 will be short-circuited, so that a pulse is produced in the winding 37, which causes the device 27 to become conductive so that the main discharge path for the capacitor 29 is through the plug connected to terminal 26.

The circuit described has a number of important advantages, Thus, in certain known circuits the voltage across a capacitor such as the capacitor 29 is sensed by a gap similar to the gap 32, and when the gap 32 breaks down the capacitor 29 discharges through it. This means that the gap 32 must handle high energies, Whereas in the current described the gap 32 only handles very small energies, and so has a long and stable life. The devices 24, 27 do of course handle the full discharge energy, but do not have to maintain a controlled breakdown characteristic, but only to act as reliable trigger devices. The circuit design is such that the relay contacts handle only small power.

It will be apparent that a number of modifications can be made to the circuit. For example, the devices 24, 27 can be provided with internal bands instead of external bands, or they can be other devices which can be triggered to render them conductive. A further modification is shown in FIGURE 2, in which the relay 1'6 and contact 39 are omitted. In this example an additional diode 45 is provided between the terminal 13 and inductor 18, and the terminals 13, 14 are connected through resistors 46, 47, to the unearthed ends of the windings 38, 40. In this arrangement, depending on which terminal 13, 14 is being used, either the first transformer or the second transformer will be saturated, which of course has the same effect as short circuiting one of the windings 38, 40'.

The invention can also be applied to circuits in which more than two plugs are to be used alternatively. This can be done for example by using one triggering device per plug with a slightly more complex relay arrangement than that shown in FIGURE 1.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A spark ignition system comprising in combination a capacitor, means for charging the capacitor to increase the voltage across the capacitor, a trigger device which when conductive permits discharge of the capacitor to produce a spark, a voltage sensitive device connected in a circuit across said capacitor so as to conduct when the voltage across the capacitor reaches a predetermined value, a transformer having its primary winding connected in series with said voltage sensitive device, and its secondary winding connected to the trigger device, said transformer being operable upon commencement of discharge of the capacitor through said voltage sensitive device to switch said trigger device to conduction, said system further including a second transformer having its primary winding connected in series with said voltage sensitive device, and its secondary winding connected to a second trigger device which when conductive permits discharge of the capacitor to produce a spark at a diiferent plug from that controlled by the first-mentioned trigger device, this system further including switch means operable to determine which trigger device is switched to conduction when the voltage sensitive device conducts.

2. A system as claimed in claim 1 in which said switch means acts to short-circuit a winding on one or other of the transformers.

3. A system as claimed in c1aim-1 in which said switch means acts to'saturate one or other of the transformers.

References Cited UNITED STATES PATENTS 2,978,611 4/1961 Segall 315183 JOHN w. HUCKERT, Primary Examiner.

J. R. SHEWMAKER, Assistant Examiner. 

